Apparatus and methods for removing contaminant particles in a plasma process

ABSTRACT

A method and apparatus for operating a plasma processing chamber includes performing a plasma process at a process pressure and a pressure power to generate a plasma. A first ramping-down stage starts in which the process power and the process pressure are ramped down substantially simultaneously to an intermediate power level and an intermediate pressure level, respectively. The intermediate power level and intermediate pressure level are preselected so as to raise a plasma sheath boundary above a threshold height from a surface of a substrate. A purge gas is flowed from a showerhead assembly at a sufficiently high rate to sweep away contaminant particles trapped in the plasma such that one or more contaminant particles move outwardly of an edge of the substrate. A second ramping-down stage starts where the intermediate power level and the intermediate pressure level decline to a zero level and a base pressure, respectively.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. provisional patent applicationSer. No. 62/633,351, filed Feb. 21, 2018, which is herein incorporatedby reference.

FIELD

The present disclosure generally relates to apparatus and methods forremoving contaminant particles in an end stage of a plasma processingoperation.

DESCRIPTION OF THE RELATED ART

In the manufacture of high density integrated circuits using a plasmaprocessing chamber, contaminant particles are derived from by-productsof reactant gases and other by-products already attached to interiorsurfaces of the plasma processing chamber. These contaminant particlesare trapped in a plasma region during a plasma process. As theprocessing ends and the plasma region collapses, the contaminantparticles fall onto the substrate, leading to a decreased yield orreduced reliability of semiconductor products formed from the substrate.

Therefore, there is a need for apparatus and methods that address thecontaminant particle issues in a plasma process.

SUMMARY

The present disclosure provides apparatus and method for removingcontaminant particles in the end stage of the plasma processing.

In one aspect, a method of operating a plasma processing chamber isprovided. The method includes performing a plasma process at a processpressure and a process power to generate plasma; ramping down theprocess power and the process pressure substantially simultaneously toan intermediate power level and an intermediate pressure level,respectively, wherein the intermediate power level and the intermediatepressure level are selected so as to raise a plasma sheath boundaryabove a threshold height from a surface of a substrate; maintaining theintermediate power level for a first time period and maintaining theintermediate pressure level for a second time period while flowing apurge gas from a showerhead assembly; and reducing the intermediatepower level and the intermediate pressure level to a zero power leveland a base pressure, respectively.

In one aspect, an apparatus for performing a plasma process is provided.The apparatus includes a processor; and a memory storing computerprogram code configured to, with the processor, cause the apparatus toperform a plasma process at a process pressure and a process power togenerate plasma in a plasma processing chamber; ramp down the processpower and the process pressure substantially simultaneously to anintermediate power level and an intermediate pressure level,respectively, wherein the intermediate power level and the intermediatepressure level are selected so as to raise a plasma sheath boundaryabove a threshold height from a surface of a substrate; maintain theintermediate power level for a first time period and maintain theintermediate pressure level for a second time period while flowing apurge gas from a showerhead assembly; and reduce the intermediate powerlevel and the intermediate pressure level to a zero power level and abase pressure, respectively.

In one aspect, an apparatus for performing a plasma process is provided.The apparatus includes a processor; and a memory storing computerprogram code configured to, with the processor, cause the apparatus toperform a plasma process at a process pressure and a process power togenerate plasma in a plasma processing chamber; select an intermediatepower level and an intermediate pressure level; ramp down the processpower and the process pressure substantially simultaneously to theintermediate power level and the intermediate pressure level,respectively; maintain the intermediate power level for a first timeperiod and maintain the intermediate pressure level for a second timeperiod while flowing a purge gas from a showerhead assembly; and reducethe intermediate power level and the intermediate pressure level.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentdisclosure can be understood in detail, a more particular description ofthe disclosure, briefly summarized above, will be provided by referenceto aspects, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlyexemplary aspects and are therefore not to be considered limiting of thescope of the disclosed and claimed aspects, and the disclosure may admitto other equally effective aspects.

FIG. 1 is a schematic sectional view of a plasma processing chamberaccording to one aspect of the present disclosure.

FIG. 2 is a flowchart illustrating operations of reducing or eliminatingcontaminant particles in accordance with one aspect of the presentdisclosure.

FIG. 3A is a graph illustrating changes of RF or AC power in transitionfrom a plasma process stage to a plasma extinguished stage in accordancewith one aspect of the present disclosure.

FIG. 3B is a graph illustrating changes of a chamber pressure intransition from a plasma process stage to a plasma extinguished stage inaccordance with one aspect of the present disclosure.

FIGS. 4A to 4C are cross-sectional views illustrating changes of aplasma in a processing volume during a transition from a plasma processstage to a plasma extinguished stage according to aspects of the presentdisclosure.

FIG. 4A illustrates a schematic cross-sectional view of the processingchamber during a plasma process stage in accordance with one aspect ofthe present disclosure.

FIG. 4B illustrates a schematic cross-sectional view of the processingchamber during an intermediate flat stage in accordance with one aspectof the present disclosure.

FIG. 4C is a schematic cross-sectional view of the processing chamberduring a plasma extinguished stage in accordance with one aspect of thepresent disclosure.

DETAILED DESCRIPTION

FIG. 1 is a schematic sectional view of a plasma processing chamber 100according to one aspect of the present disclosure. The plasma processingchamber 100 comprises a chamber 102, a showerhead assembly 104, aprocessing volume 108, a chemical delivery module 103, a plasma controlcircuit 110, a substrate support 114, and a pressure regulator 109.

Chemical delivery module 103 delivers various gases including precursorgases, carrier gases, and/or purge gases to the showerhead assembly 104from one or more gas sources. The gas sources may also supply purge gasto the showerhead assembly 104.

The showerhead assembly 104 here includes multiple processing gaschannels including a first processing gas channel 104A and a secondprocessing gas channel 104B, through which multiple process gases aredelivered to the processing volume 108 independently.

During processing thereof, a substrate 116 is disposed on the substratesupport 114 which has the capability of moving up and down in a verticaldirection 115. The substrate support 114 also includes a temperaturecontrol element, such as a heater, a plurality of cooling channels, orboth for controlling the temperature of the substrate 116.

A plurality of exhaust ports 105 are formed on an inside wall of thechamber 102 around the substrate support 114. The exhaust ports 105 areconnected to a pressure regulator 109 via one or more exhaust channels107A. The pressure regulator 109 includes a vacuum pump 107 which, inconsideration of gas(es) flowing into the showerhead, controls a chamberpressure and a rate at which the exhaust gases are drawn from thechamber.

Plasma control circuit 110 is coupled to a coil 111, and the plasmacontrol circuit 110 supplies radio frequency (RF) or other AC power tothe coil 111 to generate a plasma in the processing volume 108. The coil111 is connected to ground through a variable capacitor 112.

The plasma processing chamber 100 includes a controller 120 to controlaspects of the plasma processing chamber 100 during plasma processing.The controller 120 comprises a central processing unit (CPU) 121, amemory 122, and a support circuit 123 for the CPU 121. The controller120 facilitates control of the components of the plasma processingchamber 100. The controller 120 may be one of any form ofgeneral-purpose computers that can be used in an industrial setting forcontrolling various chamber components and sub-processors. The memory122 stores software (source or object code) that may be executed orinvoked to control the overall operations of the plasma processingchamber 100 in manners described herein. The controller 120 manipulatesrespective operations of controllable components in the plasmaprocessing chamber 100. For example, the controller 120 controls theoperations of the chemical delivery module 103, plasma control circuit110 and pressure regulator 109 for eliminating or reducing contaminantparticles in a plasma process as described herein.

During a plasma process, the chemical delivery module 103 deliversprecursor gases, carrier gases, and/or purge gases to the showerheadassembly 104 through supply lines according to the aspects of aparticular process. Subsequently, the showerhead assembly 104distributes gases across the processing volume 108. Unreacted gases, andreaction products or gas reactants, exit the plasma processing chamber100 through the exhaust ports 105.

Plasma control circuit 110 provides a radio frequency (RF) or other ACvoltage across the coil 111 to produce a voltage profile on the coil111, which generates a plasma region within the process volume 108. Byvarying the value of the variable capacitor 112, the voltage profile onthe coil 111 can be varied. Plasma control circuit 110 includes a powersupply, and may, for example, supply up to about 4000 Watts at a tunablefrequency in a range, e.g., from 50 kHz to 13.56 MHz, Other frequenciesand RF or AC powers may be provided for particular applications. In someembodiments, which may be combined with other embodiments, an additionalRF match circuit is connected to another power supply and is configuredto supply RF or AC power to a cathode equipped with an electrostaticchuck or other substrate support element to control energy of plasmaions bombarding the substrate.

FIG. 2 is a flowchart illustrating operations for reducing oreliminating contaminant particles depositing on a substrate duringplasma processing, in accordance with one aspect of the presentdisclosure.

In act 202, the plasma processing chamber performs a plasma processusing a process-specific RF or AC power and a process-specific chamberpressure. Various RF or AC power and chamber pressure levels may bespecified to generate a plasma having predetermined properties fordifferent plasma processes including, for example, a deposition processand an etching process. At the completion of the plasma process, theprocessing chamber controller turns off the supply of a processing gas,such as an etchant or deposition precursor, in act 204, and allows aninert background (e.g., carrier) or purge gas, such as argon, tocontinue to flow into the chamber.

In act 205, intermediate levels for power and pressure are preselected.It is contemplated that operation 205 may alternatively occur prior toeither or both of operations 202 and 204.

In act 206, the plasma process enters a first ramping-down stage whereone or both of the RF or AC power for a plasma and the chamber pressureare ramped down substantially simultaneously to respective preselectedintermediate levels. In some embodiments, the intermediate power levelis sufficiently high such that the plasma region is able to trap thecontaminant particles therein. In some embodiments, the intermediatepressure level is low enough such that the plasma sheath is raised abovea threshold height above the surface of the substrate on the substratesupport in the chamber. In some embodiments, the threshold height rangesfrom 0.5 mm to 2.0 mm above an upper surface of the substrate. Forexample, the threshold height may range between 1.0 mm to 1.5 mm. Insome embodiments, the threshold height is about 1.3 mm from thesubstrate.

In act 208, the RF or AC power is maintained at the intermediate powerlevel for a first time period, and the chamber pressure is maintained atthe intermediate pressure level for a second time period. During theintermediate power and pressure stages, a purge gas is flowed from theshowerhead assembly at a sufficiently high rate to sweep away thecontaminant particles trapped over the lifted plasma sheath out of theedge of the substrate. In one example, the first time period is equal tothe second time period. In another example, the first time period isgreater than or less than the second time period.

In act 210, the RF and/or other AC power and the chamber pressure aresubstantially simultaneously ramped down to the zero power level and toa base pressure, respectively. As the second ramping down stageprogresses, the plasma extinguishes and the contaminant particlesentrained in the purge gas flow exit the processing chamber through theexhaust ports.

The method 200 shown is not limited to the sequence or number of actsillustrated in FIG. 2, but may include embodiments that includere-ordering, repeating, adding, and/or removing one or more of the acts202, 204, 205, 206, 208, and/or 210.

FIG. 3A is a graph illustrating changes of RF or other AC power intransition from a plasma process stage to a plasma extinguished stage inaccordance with one aspect of the present disclosure.

The processing chamber performs a plasma process at the specified RF orAC power and chamber pressure for the process being undertaken, forexample etching or depositing of a film layer on a substrate, until theplasma process is completed. In the embodiment illustrated in FIG. 3A,the processing chamber performs a plasma process PLP-1 at a RF or ACpower (e.g., a power process value), for example, of about 150 watts anda chamber pressure (e.g., a pressure process value) of, for example, 8Torr for a predetermined time, such as about 45 seconds.

Once the plasma process PLP-1 is complete, the chamber controller turnsoff the supply of the processing gases and enters the first ramping-downstage, RF-1, where the value of the RF or AC power is ramped down fromthe process value to the intermediate power level. In some embodiments,the intermediate power level is high enough to maintain the plasma suchthat the plasma is able to contain the contaminant particles therein. Insome embodiments, which may be combined with other embodiments, theintermediate RF or AC power ranges from 40% to 60% of the RF or AC powerof the process value. For example, the intermediate power level can beabout 50% of the RF or AC power of the process value.

During the first ramping-down stage RF-1, the chamber pressure declinessubstantially simultaneously with the RF or AC power decline, so thatthe plasma in the processing volume becomes narrower in the directionorthogonal to the substrate supporting surface. The plasma widens in theradial direction of the substrate supporting surface, as the plasmasheath expands and the sheath boundary becomes raised above a thresholdheight above the substrate or above the substrate supporting surface. Asthe plasma becomes narrower in the direction orthogonal to the substratesupporting surface and wider in the radial direction of the substratesupporting surface, and as the plasma sheath is raised, the contaminantparticles are pushed outwardly, in the radial direction of the substrateor the substrate supporting surface within the plasma and are trapped inthe plasma in the region over the outer peripheral area of the substrateor the substrate supporting surface. In some embodiments, the thresholdheight, or the height of the plasma sheath boundary, is increased by 20%to 40% compared to the height of the plasma sheath boundary duringsubstrate plasma processing, e.g., the dark space thickness over thesubstrate is increased by 20% to 40% compared to the height or thicknessthereof during the plasma processing of the substrate. For example, in acase where an average height of plasma sheath is 1.0 mm from thesubstrate during the plasma process, the threshold height can be about1.3 mm from the substrate during the first stage of the particle removalprocess. As a result, the contaminant particles trapped in the plasmasheath are also lifted up from the substrate.

Once the RF or AC power has declined to the intermediate RF or AC powerlevel, the processing chamber enters the intermediate flat stage RF-2where the RF or AC power is maintained at a constant intermediate powerlevel for a first time period. The first time period of the RF-2 stagecan be a suitable period of time long enough to remove the contaminantparticles trapped in the plasma sheath. In some embodiments, the firsttime period ranges from 2 seconds to 10 seconds. In the embodimentillustrated in FIG. 3A, the first time period is about 3 seconds.

During this intermediate flat stage RF-2, the processing chamber flows apurge gas from the showerhead assembly at a sufficiently high enoughrate to sweep away the contaminant particles trapped in the plasmasheath outwardly beyond the edge of the substrate. The swept awaycontaminant particles exit the chamber through the exhaust ports.Examples of purge gases which may be used include, but are not limitedto, helium (He), argon (Ar), nitrogen (N2), hydrogen (H2), or a mixturethereof.

Once the intermediate flat stage RF-2 is complete, the processingchamber enters the second ramping-down stage RF-3 stage where the RF orAC power is reduced to the zero level substantially simultaneously withthe decline of the chamber pressure to a base pressure (e.g.;atmospheric pressure). By the end of the second ramping-down stage RF-3,the plasma is extinguished.

FIG. 3B is a graph illustrating changes of the chamber pressure intransition from a plasma process stage to a plasma extinguished stage inaccordance with one aspect of the present disclosure.

As illustrated, the processing chamber performs a plasma process PLP-1at the process power value, for example 150 watts, and a processpressure value, for example 8 Torr, for a predetermined time such asuntil the plasma process is complete. It is to be noted that otherprocess power values and other process pressure values may be used.

Once the plasma process is complete, the chamber controller turns offthe supply of the processing gas and enters the first ramping-down stageP-1 where the process pressure is ramped down to the intermediatepressure level. The first ramping-down stage P-1 for the chamberpressure can occur substantially simultaneously with the firstramping-down stage RF-1 for the RF or AC power.

The intermediate pressure level is low enough so that the plasma sheathis raised above a threshold height as described above. In someembodiments, the intermediate pressure level ranges between 40% to 60%of the process pressure used during processing of the substrate duringPLP-1. For example, the intermediate pressure level can be about 50% ofthe process pressure used during the plasma processing on the substrate.

Once the chamber pressure has declined to the intermediate pressurelevel, the processing chamber starts the intermediate flat stage P-2where the intermediate chamber pressure is maintained for a second timeperiod. The second time period of the intermediate flat stage P-2 can bea suitable period of time long enough to remove the contaminantparticles trapped in the plasma sheath by sweeping them out with a purgegas. In some embodiments, the first time period of the intermediate flatstage RF-2 is about the same as the second time period of theintermediate flat stage P-2. In some embodiments, the second time periodof P-2 stage is longer than the first time period of intermediate flatstage RF-2. In some embodiments, the second time period ranges fromabout 2 seconds to 10 seconds. In some embodiments, the second timeperiod is about 4 seconds.

During this intermediate flat stage P-2, purge gas is flowed into thechamber from the showerhead assembly at a sufficiently high rate tosweep the contaminant particles trapped in the plasma sheath outwardlyof the edge of the substrate.

Once the intermediate flat stage P-2 is complete, the processing chamberenters the second ramping-down stage P-3 stage where the chamberpressure declines to a base pressure level substantially simultaneouslyas the RF or AC power declines to about the zero level. At the end ofthe second ramping-down stage P-3, the plasma can be extinguished. Here,the base pressure refers to a chamber pressure used before a plasmaprocess starts. For example, the base pressure can be an atmosphericpressure.

FIGS. 4A to 4C are cross-sectional views illustrating changes in aprocessing volume 403 during a transition from a plasma process stage toa plasma extinguished stage according to aspects of the presentdisclosure.

FIG. 4A illustrates a schematic cross-sectional view of the processingchamber during a plasma process in accordance with one aspect of thepresent disclosure.

As illustrated, a substrate 408 is located on the substrate support 410.Then, process gases are introduced into the processing volume 403through the showerhead 402, and a specified RF or AC power and aspecified chamber pressure are applied to generate a plasma 404 betweena showerhead 402 and the substrate support 410. As a plasma processproceeds, the contaminant particles 406 can occur from, for example,by-products of reactant gases and can be trapped in a plasma 404.

FIG. 4B illustrates a schematic cross-sectional view of the processingchamber during the intermediate flat stage in accordance with one aspectof the present disclosure.

Once the plasma process is complete, the chamber controller turns offthe supply of the processing gas precursor, and the processing chamberenters the first ramping-down stage where the RF or AC power and thechamber pressure are ramped down substantially simultaneously to theintermediate power level and the intermediate pressure level.

Once the RF or AC power and the chamber pressure reach the intermediatepower level and the intermediate pressure level, respectively, theprocessing chamber enters the intermediate flat stage where theintermediate power level is maintained for the first time period, andthe intermediate pressure level is maintained for the second timeperiod. During the intermediate flat stage, the plasma 404 can becomenarrower in a direction A₁ orthogonal to a surface 411 of the substratesupport 410 and wider in a radial direction A₂ of the surface 411 of thesubstrate support 410. Additionally, the plasma sheath 414 a may raisefrom the substrate 408 as a result of a reduced RF or AC power andchamber pressure. As the plasma becomes narrower and the plasma sheathis raised, the contaminant particles move outwardly with respect to thesubstrate 408 and become located in the plasma over the outer peripheralarea of the substrate.

During the intermediate flat stage, the processing chamber flows a purgegas across the processing volume at a high rate and pumps the purge gasout through a vacuum pump so that the contaminant particles trapped inthe plasma sheath are swept away through the exhaust ports provided onthe wall around the substrate.

FIG. 4C is a schematic cross-sectional view of the processing chamber atthe plasma extinguished stage in accordance with one aspect of thepresent disclosure.

At the end of the intermediate flat stage, the processing chamber entersthe second ramping-down stage where the RF or AC power and the chamberpressure substantially simultaneously decline to the zero level and thebase pressure, respectively. At the end of the second ramping-downstage, the plasma may be extinguished and the remaining contaminantparticles 406 may exit the chamber and into exhaust ports. As a result,the plasma collapses and the contaminant particles are removed orreduced, which can prevent the remaining contaminant particles 406 fromfalling on the substrate 408.

While the foregoing is directed to aspects and embodiments of thepresent disclosure, other aspects and embodiments of the disclosure maybe devised without departing from the basic scope thereof, and the scopethereof is determined by the claims that follow.

What is claimed is:
 1. A method of operating a plasma processingchamber, the method comprising: performing a plasma process at a processpressure and a process power to generate plasma; ramping down theprocess power and the process pressure substantially simultaneously toan intermediate power level and an intermediate pressure level,respectively, wherein the intermediate power level and the intermediatepressure level are selected so as to raise a plasma sheath boundaryabove a threshold height from a surface of a substrate; maintaining theintermediate power level for a first time period and maintaining theintermediate pressure level for a second time period while flowing apurge gas from a showerhead assembly; and reducing the intermediatepower level and the intermediate pressure level to a zero power leveland a base pressure, respectively.
 2. The method of claim 1, wherein theintermediate power level is high enough such that the plasma is able tocontain one or more contaminant particles therein.
 3. The method ofclaim 1, wherein the threshold height of the plasma sheath boundary isat least 30% higher than a height of a plasma sheath boundary during theplasma process.
 4. The method of claim 1, wherein the intermediate powerlevel is between about 40% to about 60% of the process power.
 5. Themethod of claim 1, wherein the intermediate power level is about 50% ofthe process power.
 6. The method of claim 1, wherein the intermediatepressure level ranges from about 40% to about 60% of the processpressure.
 7. The method of claim 1, wherein the intermediate pressurelevel is about 50% of the process pressure.
 8. The method of claim 1,wherein the purge gas includes helium (He), argon (A nitrogen (N2),hydrogen (H2), or a mixture thereof.
 9. The method of claim 1, whereinthe purge gas exits the plasma processing chamber through one or moreexhaust ports disposed on an inside wall of the plasma processingchamber around a substrate support.
 10. The method of claim 1, whereinthe first time period is about the same as the second time period, orthe first time period is shorter than the second time period.
 11. Anapparatus for performing a plasma process, comprising: a processor; anda memory storing computer program code configured to, with theprocessor, cause the apparatus to: perform a plasma process at a processpressure and a process power to generate plasma in a plasma processingchamber; ramp down the process power and the process pressuresubstantially simultaneously to an intermediate power level and anintermediate pressure level, respectively, wherein the intermediatepower level and the intermediate pressure level are selected so as toraise a plasma sheath boundary above a threshold height from a surfaceof a substrate; maintain the intermediate power level for a first timeperiod and maintain the intermediate pressure level for a second timeperiod while flowing a purge gas from a showerhead assembly; and reducethe intermediate power level and the intermediate pressure level to azero power level and a base pressure, respectively.
 12. The apparatus ofclaim 11, wherein the intermediate power level is high enough such thatthe plasma is able to contain one or more contaminant particles therein.13. The apparatus of claim 11, wherein the threshold height of theplasma sheath boundary is at least 30% higher than a height of a plasmasheath boundary during the plasma process.
 14. The apparatus of claim11, wherein the intermediate power level ranges between about 40% toabout 60% of the process power.
 15. The apparatus of claim 11, whereinthe intermediate power level is about 50% of the process power.
 16. Theapparatus of claim 11, wherein the intermediate pressure level rangesfrom about 40% to about 60% of the process pressure.
 17. The apparatusof claim 11, wherein the intermediate pressure level is about 50% of theprocess pressure.
 18. The apparatus of claim 11, wherein the purge gasincludes helium (He), argon (Ar), nitrogen (N2), hydrogen (H2), or amixture thereof; and wherein the purge gas exits the plasma processingchamber through one or more exhaust ports disposed on an inside wall ofthe plasma processing chamber around a substrate support.
 19. Theapparatus of claim 11, wherein the first time period is about the sameas the second time period, or the first time period is shorter than thesecond time period.
 20. An apparatus for performing a plasma process,comprising: a processor; and a memory storing computer program codeconfigured to, with the processor, cause the apparatus to: perform aplasma process at a process pressure and a process power to generateplasma in a plasma processing chamber; select an intermediate powerlevel and an intermediate pressure level; ramp down the process powerand the process pressure substantially simultaneously to theintermediate power level and the intermediate pressure level,respectively; maintain the intermediate power level for a first timeperiod and maintain the intermediate pressure level for a second timeperiod while flowing a purge gas from a showerhead assembly; and reducethe intermediate power level and the intermediate pressure level.